Waterbeds today comprise a heavy vinyl mattress, usually of 20-gauge plastic, which is placed in a sturdy wood frame platform supporting a bed box comprising a continuous bottom of planks or plywood sheet and a substantial side rail perimeter frame. In the event the mattress is punctured, the water in the mattress could leak, damaging the bed frame, the floor, and other items wherever the water ran. Accordingly, a plastic safety liner sheet is usually disposed between the mattress and the frame sides and bottom before the mattress is installed and filled. This sheet is usually 8 mil vinyl plastic, and serves to contain any water which leaks from the mattress.
There are a variety of methods of manufacture and installation of waterbed safety liners in current usage. First, regarding manufacture, a principal method involves welding the corners of the liner to form a box corner. An appropriately sized sheet of plastic is folded diagonally to form a triangle, and an induction welding machine is used to form a weld line along the two folded corners parallel to the two sides (not the hypotenuse) of the triangle, and the small triangular scraps are cut off and discarded as waste. The sheet is then folded diagonally the other way and induction welded to form the other two corners.
Second, as to installation, this corner-welded box liner is then shipped to the customer's installation site where a variety of installation methods are employed. Usually, the vertical sides of the safety liner are higher than the frame side. In one installation, the excess height is cut off, or folded over, below the side frame top edge, and taped in place. Alternately, the box liner may be stapled in place along its upper edge. Or, strips of wood may be nailed over the upper edge of the liner. Still another method involves cutting strips of cardboard from packing boxes, placing them adjacent the frame sides, tucking excess liner material over the top of the cardboard and between it and the frame sides, then securing it to the frame sides (by taping, tacking, or stapling through the liner and cardboard). In some instances such securing means are omitted, but keeping the liner in place while installing and filling the mattress is tricky.
Recently, the "Tuckaliner" (U.S. Pat. No. 3,973,282) has become employed as an installation device and method. The "Tuckaliner" is a strip of resilient material, e.g., a plastic, having a first rolled longitudinal edge, a second longitudinal flat edge, and a bowed portion therebetween. The strips of the "Tuckaliner" are cut in the field to the bed length and width, and installed by nailing or stapling it midway up the frame sides with the rolled edge at the upper edge desired for the top of the safety liner. The welded box corner liner is then fitted into the bed frame, and the excess of the side risers are tucked in behind the rolled edge of the "Tuckaliner." The bow portion keeps the liner in place against the frame side by its spring action.
All these taping, tacking, stapling or cut cardboard field installations are time consuming, labor intensive, and therefore expensive. Further, where stapling or tacking is used, the liner is punctured below its upper edge, permitting some leakage possibilities.
A less field-labor intensive liner unit is the "Delta Star" type (made by Del Astra Industries, Stockton, CA). This is a welded, fitted liner that has rigid supporting strips self-contained in double side walls of plastic sheeting. The plastic sheeting completely surrounds the supporting strips, and the sheeting is then welded at the exterior bottom edge all around the periphery. Four or eight support strips are used, one or two along each side and the ends, and they are not joined at the corners. While this system is fast to install in the field, it is expensive to make as it requires more plastic sheeting, use of expensive welding equipment, and more factory labor.
Another field installation method involves making a hospital corner in the liner plastic at each corner of the bed frame followed by taping or stapling it to the bed frame. The hospital corner is a method of field forming a relatively neat corner as compared to a manufactured, induction-welded box corner. This corner forming and securing is field-labor intensive and expensive. Field labor is usually more expensive than factory labor.
Accordingly, there is a need for a waterbed liner unit that can be easily made in the factory to precise dimensions, and which does not involve use of expensive induction welding equipment, yet which unit has free-standing, self-supporting side walls for easy and quick field installation, without the disadvantages of time and materials expense of employing securing means.